In a communication system, to ensure that uplink signals sent by all UEs (User Equipment, user equipment) that are served by a base station can synchronously reach the base station, which is described in this application document by taking an evolved NodeB (eNodeB) as an example, and in an uplink transmission process, the eNodeB adjusts TA (Timing Advance, timing advance) values for the UEs according to offset conditions of the uplink signals.
In a system that brings in a CA (Carrier Aggregation, carrier aggregation) feature, a UE may communicate with an eNodeB through multiple CCs (Component Carrier, component carrier) in an uplink and a downlink, respectively. For a UE, if the eNodeB considers that these CCs may share a TA value, that is, the eNodeB adjusts the TA value only by referring to any one of uplink transmission signals in these CCs; the TA value may be used by these CCs, and these CCs are considered to belong to a TA group. Under ordinary circumstances, if one or several certain CCs among these CCs are performed signal amplification when passing through a frequency selective repeater (Repeater) of a certain frequency, while another one or several CCs do not pass through a repeater for signal amplification or are performed signal amplification when passing through a frequency selective repeater of another certain frequency, and when the UE falls into the coverage of one of the repeaters or falls into the coverage of two repeaters, respectively, TA values of these CCs cannot be shared, that is, these CCs do not belong to the same TA group. While if all these CCs do not pass through a repeater for amplification or they are performed signal amplification when passing through frequency selective repeaters of the same frequency, it may be considered that these CCs may share the same TA value, that is, the CCs belong to the same TA group.
For the UE and the eNodeB that support CA, when the UE enters a connection state, and the eNodeB decides to allocate more CCs for the UE, an RRC (Radio Resource Control, radio resource control) connection reconfiguration message is used to add one or multiple CCs for the UE, and related attribute information of the CC is provided in the message. When the eNodeB decides to add one or multiple CCs for the UE, the UE is required to execute a random access process on a CC every time when the CC is added, so that the eNodeB judges whether the CC can share a TA value with at least one CC of current communication.
The inventor finds that, in the prior art, every time when the CC is added, frequent random access may be caused, which causes interference in random access resources, thereby increasing conflict probability of the random access process.